1. Field of the Invention
The present invention relates to an apparatus and a method for reproducing a multi-layer disc which has a first layer containing low-quality recorded data and a second layer containing high-quality recorded data, and more particularly to those capable of comparing such high-quality and low-quality data with each other.
2. Description of the Related Art
There is currently proposed a novel type of optical disc termed DVD (Digital Versatile Disc) greater in capacity than the known compact disc (hereinafter referred to as CD).
On a DVD which is an optical disc of 12 cm in diameter, information is recorded at a track pitch of 0.8 .mu.m narrower than an ordinary track pitch of 1.6 .mu.M employed on the conventional CD, and the wavelength of a semiconductor laser is changed from 780 nm on the CD to 630 nm, and the EFM (Eight-to-Fourteen Modulation) adopted for the CD is improved to consequently realize high-density recording which corresponds to information of approximately 4 G bytes on one side of the disc.
Relative to such DVD, a multi-layer structure having two recording layers is lately proposed.
As disclosed, for example, in U.S. Pat. No. 5,706,263 filed on Mar. 26, 1997, the present applicant proposed a high-quality digital audio disc having a multi-layer structure where a 16-bit digital audio signal sampled at a frequency of 44.1 kHz is recorded in one layer, while 1-bit quantized digital audio signal is recorded in another layer after being processed through .SIGMA..DELTA. modulation at a very high sampling frequency of 2.842 MHz which is 16 times the above frequency of 44.1 kHz.
The contents of signals to be recorded in such two layers are mutually the same (e.g., same music piece). Therefore, data of the same contents are recorded as normal-quality data of a CD level in one layer while being recorded as higher-quality data in the other layer.
Since such a multi-layer disc has one layer containing a recorded 16-bit digital audio signal sampled at 44.1 kHz, it is reproducible by any of ordinary compact disc players available currently in the general market.
Further in any apparatus adapted for reproduction of both layers, signals are reproducible properly from the two layers, so that any of a multiplicity of compact discs diffused widely now can be reproduced and still the novel multi-layer disc mentioned above can be reproduced as well.
Any of compact discs available in general and the novel multi-layer disc are substantially the same in external appearance. And in one of the layers of the multi-layer disc, data is recorded in conformity with the format of a compact disc so as to maintain down-compatibility therewith, i.e., digital audio signal processed through sampling at 44.1 kHz, 16-bit quantization and EFM is recorded.
For the purpose of explanatory convenience in the following description, one layer containing recorded data of the CD format will be referred to as a CD layer, and another layer containing recorded 1-bit digital audio signal processed at a sampling frequency of 2.842 MHz through .SIGMA..DELTA. modulation will be referred to as an HD (High-Definition) layer.
In comparing the tone qualities of different types of recording media, i. e., when reproducing the same music piece or the like from two recording media of an analog record and a compact disc for example to evaluate the tone qualities thereof, it has been necessary heretofore to execute the customary procedure of first connecting a record player and a compact disc (CD) player to an amplifier, then, during the operation of the record player, holding the CD player under control in a reproduction standby mode, and upon completion of reproducing the music or the like from the record for a predetermined time, switching a selector from the record to the CD, and driving the CD player to reproduce the music from the CD.
Thus, the user is compelled to perform such complicated manipulation and, since continuous switching from a record to a CD cannot be carried out successively, it has been impossible heretofore to achieve perfect evaluation of the reproduced tones which are temporally continuous.
Meanwhile, if audition in sales shops or stores for example can be simplified to facilitate evaluation of the tone qualities obtained from both layers of the multi-layer disc, then a remarkable convenience will be ensured with another advantage of promoting sales.
In comparing the contents of such multi-layer disc, if the 1-bit digital audio signal processed through .SIGMA..DELTA. modulation at 2.842 MHz can be reproduced immediately after the 16-bit digital audio signal sampled at 44.1 kHz is once reproduced for a predetermined time, then the desired aural comparison can be effected in time series successively to thereby attain exact and convenient comparison of the audio qualities.